There is a manufacturing method employing a metal-based composite material for raising the strength of a specific portion of a product. For example, Japanese Patent Laid-Open Publication JP-A-2001-316740 discloses a method of manufacturing a pulley which employs a metal-based composite material for any portion requiring strength, while using an ordinary metal for any other portion not requiring high strength, in order to achieve strength and a reduction in production cost. This method of manufacturing a pulley will be described with reference to FIG. 21 hereof.
The pulley 301 shown in FIG. 21 has a hub 302 formed from a composite material in its center, an aluminum alloy disk 303 formed integrally with the hub 302 and a grooved portion 305 fitted about the disk 303 with a shock absorbing member 304 held therebetween, and the hub 302 of high strength can bear a bolt tightening force applied for attaching the pulley 301 to a shaft.
The method of manufacturing the pulley 301 is started by extrusion molding a composite material into a cylinder and cutting the cylinder to form the hub 302. Then, the hub 302 is set in a pulley casting mold and the mold is filled with a molten aluminum alloy.
The method of manufacturing a pulley as described, however, requires a great deal of time and labor, since it requires steps for making two parts separately, i.e. the hub 302 of a composite material and the aluminum alloy disk 303. The step of forming the hub 302 of a composite material and the step of casting the aluminum alloy disk 303 have both the drawback of involving a complicated job and requiring a great deal of time and labor.
A method of manufacturing a composite material having an improved cooling property by using a metal-based composite material is disclosed in, for example, Japanese Patent Publication JP-A-2002-66724. This manufacturing method is an art characterized by pressing a block of a metal-based composite material in a press to separate the matrix and reinforcing material in the metal-based composite material from each other and thereby situate the reinforcing material in a pattern lacking uniformity, so that the thermal conductivity of the reinforcing material situated in a pattern lacking uniformity may improve the cooling property of the product. The method of manufacturing the composite material will now be described with reference to FIGS. 22A, 22B and 22C hereof.
A product 311 formed from a composite material as shown in FIG. 22A includes a base portion 312 and a plurality of fins 313 formed on a surface of the base portion 312.
Firstly, a metal-based composite material 314 is produced from an aluminum alloy 315 and fine particles 316 of silicon carbide and the metal-based composite material 314 as produced is used to form a block 317, as shown in FIG. 22B. Secondly, the block 317 is heated, placed in a mold 318 (having cavities 319 for fins) and compressed.
When it is compressed as shown in FIG. 22C, the aluminum alloy 315 flows into the cavities 319 for fins and forms aluminum alloy fins 313.
According to the method of manufacturing the composite material as described, however, fine particles of silicon carbide cannot be put in the fins 313 adequately, but the fins 313 are only of the aluminum alloy and too low in strength, though a certain amount of time and labor can be saved. In other words, it is impossible to have silicon carbide distributed in the center of the fins 313 to achieve any desired volume content and as a result, it is difficult to rely on the strength of the composite material.
Therefore, there is a desire for an art which facilitates the manufacture of a product of a metal-based composite material having a ceramic volume content differing from one portion to another.